The 51-page report by van Schewick details the problems with Binge On in great detail, noting that it falls afoul of the FCC's transparency rules, that it unfairly picks winners and losers and that it harms competition. The core argument:

Binge On undermines the core vision of net neutrality: Internet service providers (ISPs) that
connect us to the Internet should not act as gatekeepers that pick winners and losers online by
favoring some applications over others. By exempting Binge On video from using customers’ data
plans, T-Mobile is favoring video from the providers it adds to Binge On over other video.

T-Mobile says that it does not intend to become a gatekeeper on the Internet: It says Binge On is
open to all legal video streaming providers at no cost, as long as they can meet some “simple
technical requirements.” The idea is that any discriminatory effects of Binge On disappear as more
providers join the program. However, the technical requirements published on T-Mobile’s website
are substantial. They categorically exclude providers that use the User Datagram Protocol (UDP),
making it impossible for innovative providers such as YouTube to join. They discriminate against
providers that use encryption, a practice that is becoming the industry standard. While some
providers can join easily, a significant number will need to work with T-Mobile to determine
whether their service can be part of Binge On. Many will have to invest time and resources to
adapt their service to T-Mobile’s systems. The smaller the provider, the longer it will likely take
for T-Mobile to get to it.

The result: Binge On allows some providers to join easily and creates lasting barriers for others,
especially small players, non-commercial providers, and start-ups. As such, the program harms
competition, user choice, free expression, and innovation.

What's perhaps even more interesting is that van Schewick includes in the report alternatives that T-Mobile could have adopted that would have created similar plans that actually benefit consumers without messing up net neutrality:

Binge on in its current form violates net neutrality. However, T-Mobile could offer alternative
innovative plans that benefit customers and allow the ISP to compete without violating net
neutrality. For example, T-Mobile could offer customers a zero-rated low-bandwidth mode at the
same speed as Binge On, but contrary to Binge On, customers would be able to use this mode to
watch video or do anything else online. It would be their choice.

Alternatively, T-Mobile could allow customers unlimited access to the entire Internet after
customers reach their cap, just at a slower speed – the same speed currently offered through Binge
On. After reaching their cap, customers could watch video or do anything else online; again it
would be their choice. This option offers customers truly unlimited video, unlike Binge On.
Contrary to advertising, Binge On video is limited: Customers can watch video included in the
program only until they reach their monthly data cap through other Internet uses that are not zerorated.
As such, advertising Binge On as “unlimited” video might violate the FCC’s transparency
rule, which requires ISPs to accurately describe their service. In contrast, this alternative option
would allow T-Mobile to offer “unlimited video streaming” that stands up to its name and respects
net neutrality.

Finally, T-Mobile could increase the monthly data caps on its capped plans to account for the
average amount of video that people are watching. Customers could use that additional bandwidth
to do anything online, including watching video. Again, it would be their choice. All of these
alternative plans are entirely consistent with net neutrality.